Identifying the Breast Cancer Target for Indole-3-Carbinol

Institution: University of California, Berkeley
Investigator(s): Urmi Chatterji, Ph.D. -
Award Cycle: 2000 (Cycle VI) Grant #: 6FB-0025 Award: $40,000
Award Type: Postdoctoral Fellowship
Research Priorities
Detection, Prognosis and Treatment>Innovative Treatment Modalities: search for a cure

Initial Award Abstract (2000)
Current therapeutics to treat breast cancer, such as tamoxifen and Herceptin, are limited because only a minority of cancers have the target proteins for each drug. For example, tamoxifen is effective only against the 30% of breast cancers that are estrogen receptor positive. Thus, our laboratory’s interest is to identify potential therapeutics with, (i) with a more broad spectrum effectiveness, (ii) having a role both in treatment and prevention, and (iii) being tolerable with respect to unwanted side-effects. These interests led to our previous studies on a natural dietary compound found in vegetables such as broccoli and cabbage, called indole-3-carbinol (I3C). This compound and more potent derivatives will impede the growth of breast cancer cells by directly interfering with the cellular events leading to cell division. I3C will arrest cells at critical cell cycle checkpoints that are controlled by proteins (cyclins) that become unregulated in cancer. Importantly, I3C appears to inhibit both tamoxifen-sensitive and resistant breast cancer cells.

However, we still know little about the cellular binding target(s) of I3C. My hypothesis is that I3C binds to a discrete target protein in human breast cancer cells. My plan is to first identify and purify the immediate target protein of I3C from MCF7 breast cancer cells. We are hopeful that the recently discovered derivatives of I3C will have sufficient affinity to allow direct biochemical purification using affinity chromatography. We plan to clone and sequence our I3C target protein by traditional biochemical methods. To validate our protein we can use I3C-unresponsive breast cancer cells, such as MCF-10. Introduction of the I3C-binding protein into these cells should restore I3C-sensitivity.

We are hopeful that these studies will provide insight into common features of breast cancer cells to allow more effective regulation of growth control. This will eventually lead to more broad-spectrum therapeutics. In the case of I3C and its derivatives, they could find application as a primary, an adjunct, or as a preventative treatment to combat breast cancer.

Final Report (2001)
Note: The PI resigned the project after one year to accept other funding.

The primary aim of this project was to identify and purify the I3C target protein and characterize its role in the growth inhibitory functions in breast cancer cells. The first experiment undertaken was to determine the subcellular localization of the I3C target protein. Subsequently, radioligand binding assays were carried out by incubating 3H-labeled I3C with the various subcellular fractions of MCF-7 cells. The results revealed that 3H-I3C bound specifically to proteins in the nuclear extracts and binding of 3H-I3C to the nuclear proteins could be competed off with 5000-fold excess unlabeled I3C. In contrast, no significant binding of labeled I3C was evident with the microsomal or cytosolic fractions. Based on the above information, the present goal is to design and prepare an I3C-affinity column in order to purify the I3C-target protein from the nuclear fraction of MCF-7 breast cancer cells.